What alloy is 718?

718 is short-hand for a high strength, high performance nickel-based alloy better known as Inconel 718, UNS N07718 or DIN 2.4668. Inconel is a trademark of Special Metals Corporation and is applied to a range of alloys they originally developed which are all nickel-based, primarily alloyed with chromium.

Inconel 718 was introduced in the 1960s and initially used in the aerospace industry as a high strength grade, with most of that strength retained at high temperature. Nickel alloys such as Inconel 718 are well-suited to high-temperature applications as most other metals are either brittle or oxidize when exposed to elevated temperatures. However, nickel-based alloys will quickly form a protective oxide layer when heated in an atmosphere containing oxygen, thereby preventing further oxidation. Therefore, the high strength and high temperature resistance of Alloy 718 allows it to withstand the aggressive environment seen in applications such as gas turbines, jet engines, and nuclear reactors.

Due to its ready availability in the market, Alloy 718 it was taken up by the oil and gas industry. This was associated with wells moving offshore, drilling deeper with higher temperatures, pressures and corrosive contaminants. Other nickel-based alloys such as Hastelloy C276 and other Inconel alloys (such as Inconel 625) provided sufficient corrosion resistance, but insufficient strength without extensive cold working. Martensitic stainless steels were limited by their potential for hydrogen embrittlement and stress corrosion cracking. Therefore, Inconel 718 quickly became a default choice for many pressure-containing and load-bearing components in aggressive environments.

Langley Alloys stocks Alloy 718 as round bars from 1/2”-10” diameter (12.7-254mm).

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